IB/qib: Fix M_Key field in SubnGet and SubnGetResp MADs

Set the M_Key field in SubnGet and SugnGetResp MADs based on correctly
interpreting the protection level specified in the M_KeyProtBits field.

Signed-off-by: Mitko Haralanov <mitko@qlogic.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>